IO::Socket::SSL(3) User Contributed Perl Documentation IO::Socket::SSL(3)
NAME
IO::Socket::SSL -- SSL sockets with IO::Socket interface
SYNOPSIS
use strict;
use IO::Socket::SSL;
# simple HTTP client -----------------------------------------------
my $sock = IO::Socket::SSL->new(
# where to connect
PeerHost => "www.example.com",
PeerPort => "https",
# certificate verification
SSL_verify_mode => SSL_VERIFY_PEER,
# location of CA store
# need only be given if default store should not be used
SSL_ca_path => '/etc/ssl/certs', # typical CA path on Linux
SSL_ca_file => '/etc/ssl/cert.pem', # typical CA file on BSD
# easy hostname verification
SSL_verifycn_name => 'foo.bar', # defaults to PeerHost
SSL_verifycn_schema => 'http',
# SNI support
SSL_hostname => 'foo.bar', # defaults to PeerHost
) or die "failed connect or ssl handshake: $!,$SSL_ERROR";
# send and receive over SSL connection
print $client "GET / HTTP/1.0\r\n\r\n";
print <$client>;
# simple server ----------------------------------------------------
my $server = IO::Socket::SSL->new(
# where to listen
LocalAddr => '127.0.0.1',
LocalPort => 8080,
Listen => 10,
# which certificate to offer
# with SNI support there can be different certificates per hostname
SSL_cert_file => 'cert.pem',
SSL_key_file => 'key.pem',
) or die "failed to listen: $!";
# accept client
my $client = $server->accept or die
"failed to accept or ssl handshake: $!,$SSL_ERROR";
# Upgrade existing socket to SSL ---------------------------------
my $sock = IO::Socket::INET->new('imap.example.com:imap');
# ... receive greeting, send STARTTLS, receive ok ...
IO::Socket::SSL->start_SSL($sock,
SSL_verify_mode => SSL_VERIFY_PEER,
SSL_ca_path => '/etc/ssl/certs',
...
) or die "failed to upgrade to SSL: $SSL_ERROR";
# manual name verification, could also be done in start_SSL with
# SSL_verifycn_name etc
$client->verify_hostname( 'imap.example.com','imap' )
or die "hostname verification failed";
# all data are now SSL encrypted
print $sock ....
DESCRIPTION
This module provides an interface to SSL sockets, similar to other
IO::Socket modules. Because of that, it can be used to make existing
programs using IO::Socket::INET or similar modules to provide SSL
encryption without much effort. IO::Socket::SSL supports all the extra
features that one needs to write a full-featured SSL client or server
application: multiple SSL contexts, cipher selection, certificate
verification, Server Name Indication (SNI), Next Protocol Negotiation
(NPN), SSL version selection and more.
If you have never used SSL before, you should read the appendix
labelled 'Using SSL' before attempting to use this module.
If you are trying to use it with threads see the BUGS section.
METHODS
IO::Socket::SSL inherits from another IO::Socket module. The choice of
the super class depends on the installed modules:
o If IO::Socket::IP with at least version 0.20 is installed it will
use this module as super class, transparently providing IPv6 and
IPv4 support.
o If IO::Socket::INET6 is installed it will use this module as super
class, transparently providing IPv6 and IPv4 support.
o Otherwise it will fall back to IO::Socket::INET, which is a perl
core module. With IO::Socket::INET you only get IPv4 support.
Please be aware, that with the IPv6 capable super classes, it will
lookup first for the IPv6 address of a given hostname. If the resolver
provides an IPv6 address, but the host cannot be reached by IPv6, there
will be no automatic fallback to IPv4. To avoid these problems you can
either force IPv4 by specifying and AF_INET as "Domain" of the socket
or globally enforce IPv4 by loading IO::Socket::SSL with the option
'inet4'.
IO::Socket::SSL will provide all of the methods of its super class, but
sometimes it will override them to match the behavior expected from SSL
or to provide additional arguments.
The new or changed methods are described below, but please read also
the section about SSL specific error handling.
new(...)
Creates a new IO::Socket::SSL object. You may use all the friendly
options that came bundled with IO::Socket::INET, plus (optionally)
the ones that follow:
SSL_hostname
This can be given to specify the hostname used for SNI, which is
needed if you have multiple SSL hostnames on the same IP address.
If not given it will try to determine hostname from PeerAddr,
which will fail if only IP was given or if this argument is used
within start_SSL.
If you want to disable SNI set this argument to ''.
Currently only supported for the client side and will be ignored
for the server side.
See section "SNI Support" for details of SNI the support.
SSL_version
Sets the version of the SSL protocol used to transmit data.
'SSLv23' auto-negotiates between SSLv2 and SSLv3, while 'SSLv2',
'SSLv3', 'TLSv1', 'TLSv1_1' or 'TLSv1_2' restrict the protocol to
the specified version. All values are case-insensitive. Instead
of 'TLSv1_1' and 'TLSv1_2' one can also use 'TLSv11' and
'TLSv12'. Support for 'TLSv1_1' and 'TLSv1_2' requires recent
versions of Net::SSLeay and openssl.
You can limit to set of supported protocols by adding !version
separated by ':'.
The default SSL_version is defined by underlying cryptographic
library. E.g. 'SSLv23:!SSLv2' means, that SSLv2, SSLv3 and TLSv1
are supported for initial protocol handshakes, but SSLv2 will not
be accepted, leaving only SSLv3 and TLSv1. You can also use
!TLSv1_1 and !TLSv1_2 to disable TLS versions 1.1 and 1.2 while
allowing TLS version 1.0.
Setting the version instead to 'TLSv1' will probably break
interaction with lots of clients which start with SSLv2 and then
upgrade to TLSv1. On the other side some clients just close the
connection when they receive a TLS version 1.1 request. In this
case setting the version to 'SSLv23:!SSLv2:!TLSv1_1:!TLSv1_2'
might help.
SSL_cipher_list
If this option is set the cipher list for the connection will be
set to the given value, e.g. something like 'ALL:!LOW:!EXP:!ADH'.
Look into the OpenSSL documentation
(<http://www.openssl.org/docs/apps/ciphers.html#CIPHER_STRINGS>;)
for more details.
If this option is not set or is set to '', OpenSSL builtin
default (whatever this is) will be used.
SSL_honor_cipher_order
If this option is true the cipher order the server specified is
used instead of the order proposed by the client. To mitigate
BEAST attack you might use something like
SSL_honor_cipher_order => 1,
SSL_cipher_list => 'RC4-SHA:ALL:!ADH:!LOW',
SSL_use_cert
If this is true, it forces IO::Socket::SSL to use a certificate
and key, even if you are setting up an SSL client. If this is
set to 0 (the default), then you will only need a certificate and
key if you are setting up a server.
SSL_use_cert will implicitly be set if SSL_server is set. For
convenience it is also set if it was not given but a cert was
given for use (SSL_cert_file or similar).
SSL_server
Set this option to a true value, if the socket should be used as
a server. If this is not explicitly set it is assumed, if the
Listen parameter is given when creating the socket.
SSL_cert_file
If your SSL certificate is not in the default place
(certs/server-cert.pem for servers, certs/client-cert.pem for
clients), then you should use this option to specify the location
of your certificate. A certificate is usually needed for an SSL
server, but might also be needed, if the client should authorize
itself with a certificate.
If your SSL server should be able to use different certificates
on the same IP address, depending on the name given by SNI, you
can use a hash reference instead of a file with "<hostname ="
cert_file>>.
Examples:
SSL_cert_file => 'mycert.pem'
SSL_cert_file => {
"foo.example.org" => 'foo.pem',
"bar.example.org" => 'bar.pem',
# used when nothing matches or client does not support SNI
'' => 'default.pem',
}
SSL_cert
This option can be used instead of "SSL_cert_file" to specify the
certificate.
Instead with a file the certificate is given as an X509* object
or array of X509* objects, where the first X509* is the internal
representation of the certificate while the following ones are
extra certificates. The option is useful if you create your
certificate dynamically (like in a SSL intercepting proxy) or get
it from a string (see openssl PEM_read_bio_X509 etc for getting a
X509* from a string).
For SNI support a hash reference can be given, similar to the
"SSL_cert_file" option.
SSL_key_file
If your RSA private key is not in default place
(certs/server-key.pem for servers, certs/client-key.pem for
clients), then this is the option that you would use to specify a
different location. Keys should be PEM formatted, and if they
are encrypted, you will be prompted to enter a password before
the socket is formed (unless you specified the SSL_passwd_cb
option).
For SNI support a hash reference can be given, similar to the
"SSL_cert_file" option.
SSL_key
This option can be used instead of "SSL_key" to specify the
certificate. Instead of a file an EVP_PKEY* should be given.
This option is useful if you don't have your key in a file but
create it dynamically or get it from a string (see openssl
PEM_read_bio_PrivateKey etc for getting a EVP_PKEY* from a
string).
For SNI support a hash reference can be given, similar to the
"SSL_key" option.
SSL_dh_file
If you want Diffie-Hellman key exchange you need to supply a
suitable file here or use the SSL_dh parameter. See dhparam
command in openssl for more information. To create a server
which provides perfect forward secrecy you need to either give
the DH parameters or (better, because faster) the ECDH curve.
SSL_dh
Like SSL_dh_file, but instead of giving a file you use a
preloaded or generated DH*.
SSL_ecdh_curve
If you want Elliptic Curve Diffie-Hellmann key exchange you need
to supply the OID or NID of a suitable curve (like 'prime256v1')
here. To create a server which provides perfect forward secrecy
you need to either give the DH parameters or (better, because
faster) the ECDH curve.
SSL_passwd_cb
If your private key is encrypted, you might not want the default
password prompt from Net::SSLeay. This option takes a reference
to a subroutine that should return the password required to
decrypt your private key.
SSL_ca_file
If you want to verify that the peer certificate has been signed
by a reputable certificate authority, then you can use this
option to locate the file containing the certificate(s) of the
reputable certificate authorities if it is not already in the
file certs/my-ca.pem or in a system-wide certificate authority
certificates store. If you definitely want no SSL_ca_file used
you should set it to undef.
SSL_ca_path
If you are unusually friendly with the OpenSSL documentation, you
might have set yourself up a directory containing several trusted
certificates as separate files as well as an index of the
certificates. If you want to use that directory for validation
purposes, and that directory is not ca/, then use this option to
point IO::Socket::SSL to the right place to look. If you
definitely want no SSL_ca_path used you should set it to undef.
SSL_verify_mode
This option sets the verification mode for the peer certificate.
You may combine SSL_VERIFY_PEER (verify_peer),
SSL_VERIFY_FAIL_IF_NO_PEER_CERT (fail verification if no peer
certificate exists; ignored for clients), SSL_VERIFY_CLIENT_ONCE
(verify client once; ignored for clients). See OpenSSL man page
for SSL_CTX_set_verify for more information.
The default is SSL_VERIFY_NONE for server (e.g. no check for
client certificate). For historical reasons the default for
client is currently also SSL_VERIFY_NONE, but this will change to
SSL_VERIFY_PEER in the near future. To aid transition a warning
is issued if the client is used with the default SSL_VERIFY_NONE,
unless SSL_verify_mode was explicitly set by the application.
SSL_verify_callback
If you want to verify certificates yourself, you can pass a sub
reference along with this parameter to do so. When the callback
is called, it will be passed:
1. a true/false value that indicates what OpenSSL thinks of the
certificate,
2. a C-style memory address of the certificate store,
3. a string containing the certificate's issuer attributes and
owner attributes, and
4. a string containing any errors encountered (0 if no errors).
5. a C-style memory address of the peer's own certificate
(convertible to PEM form with
Net::SSLeay::PEM_get_string_X509()).
The function should return 1 or 0, depending on whether it thinks
the certificate is valid or invalid. The default is to let
OpenSSL do all of the busy work.
The callback will be called for each element in the certificate
chain.
See the OpenSSL documentation for SSL_CTX_set_verify for more
information.
SSL_verifycn_scheme
Set the scheme used to automatically verify the hostname of the
peer. See the information about the verification schemes in
verify_hostname.
The default is undef, e.g. to not automatically verify the
hostname. If no verification is done the other SSL_verifycn_*
options have no effect, but you might still do manual
verification by calling verify_hostname.
SSL_verifycn_name
Set the name which is used in verification of hostname. If
SSL_verifycn_scheme is set and no SSL_verifycn_name is given it
will try to use the PeerHost and PeerAddr settings and fail if no
name can be determined.
Using PeerHost or PeerAddr works only if you create the
connection directly with "IO::Socket::SSL->new", if an
IO::Socket::INET object is upgraded with start_SSL the name has
to be given in SSL_verifycn_name.
SSL_check_crl
If you want to verify that the peer certificate has not been
revoked by the signing authority, set this value to true. OpenSSL
will search for the CRL in your SSL_ca_path, or use the file
specified by SSL_crl_file. See the Net::SSLeay documentation for
more details. Note that this functionality appears to be broken
with OpenSSL < v0.9.7b, so its use with lower versions will
result in an error.
SSL_crl_file
If you want to specify the CRL file to be used, set this value to
the pathname to be used. This must be used in addition to
setting SSL_check_crl.
SSL_reuse_ctx
If you have already set the above options (SSL_version through
SSL_check_crl; this does not include SSL_cipher_list yet) for a
previous instance of IO::Socket::SSL, then you can reuse the SSL
context of that instance by passing it as the value for the
SSL_reuse_ctx parameter. You may also create a new instance of
the IO::Socket::SSL::SSL_Context class, using any context options
that you desire without specifying connection options, and pass
that here instead.
If you use this option, all other context-related options that
you pass in the same call to new() will be ignored unless the
context supplied was invalid. Note that, contrary to versions of
IO::Socket::SSL below v0.90, a global SSL context will not be
implicitly used unless you use the set_default_context()
function.
SSL_create_ctx_callback
With this callback you can make individual settings to the
context after it got created and the default setup was done. The
callback will be called with the CTX object from Net::SSLeay as
the single argument.
Example for limiting the server session cache size:
SSL_create_ctx_callback => sub {
my $ctx = shift;
Net::SSLeay::CTX_sess_set_cache_size($ctx,128);
}
SSL_session_cache_size
If you make repeated connections to the same host/port and the
SSL renegotiation time is an issue, you can turn on client-side
session caching with this option by specifying a positive cache
size. For successive connections, pass the SSL_reuse_ctx option
to the new() calls (or use set_default_context()) to make use of
the cached sessions. The session cache size refers to the number
of unique host/port pairs that can be stored at one time; the
oldest sessions in the cache will be removed if new ones are
added.
This option does not effect the session cache a server has for
it's clients, e.g. it does not affect SSL objects with SSL_server
set.
SSL_session_cache
Specifies session cache object which should be used instead of
creating a new. Overrules SSL_session_cache_size. This option
is useful if you want to reuse the cache, but not the rest of the
context.
A session cache object can be created using
"IO::Socket::SSL::Session_Cache->new( cachesize )".
Use set_default_session_cache() to set a global cache object.
SSL_session_id_context
This gives an id for the servers session cache. It's necessary if
you want clients to connect with a client certificate. If not
given but SSL_verify_mode specifies the need for client
certificate a context unique id will be picked.
SSL_error_trap
When using the accept() or connect() methods, it may be the case
that the actual socket connection works but the SSL negotiation
fails, as in the case of an HTTP client connecting to an HTTPS
server. Passing a subroutine ref attached to this parameter
allows you to gain control of the orphaned socket instead of
having it be closed forcibly. The subroutine, if called, will be
passed two parameters: a reference to the socket on which the SSL
negotiation failed and the full text of the error message.
SSL_npn_protocols
If used on the server side it specifies list of protocols
advertised by SSL server as an array ref, e.g.
['spdy/2','http1.1']. On the client side it specifies the
protocols offered by the client for NPN as an array ref. See
also method next_proto_negotiated.
Next Protocol Negotioation (NPN) is available with Net::SSLeay
1.46+ and openssl-1.0.1+. To check support you might call
"IO::Socket::SSL-"can_npn()>. If you use this option with an
unsupported Net::SSLeay/OpenSSL it will throw an error.
close(...)
There are a number of nasty traps that lie in wait if you are not
careful about using close(). The first of these will bite you if
you have been using shutdown() on your sockets. Since the SSL
protocol mandates that a SSL "close notify" message be sent before
the socket is closed, a shutdown() that closes the socket's write
channel will cause the close() call to hang. For a similar reason,
if you try to close a copy of a socket (as in a forking server) you
will affect the original socket as well. To get around these
problems, call close with an object-oriented syntax (e.g.
$socket->close(SSL_no_shutdown => 1)) and one or more of the
following parameters:
SSL_no_shutdown
If set to a true value, this option will make close() not use the
SSL_shutdown() call on the socket in question so that the close
operation can complete without problems if you have used
shutdown() or are working on a copy of a socket.
SSL_fast_shutdown
If set to true only a unidirectional shutdown will be done, e.g.
only the close_notify (see SSL_shutdown(3)) will be called.
Otherwise a bidirectional shutdown will be done. If used within
close() it defaults to true, if used within stop_SSL() it
defaults to false.
SSL_ctx_free
If you want to make sure that the SSL context of the socket is
destroyed when you close it, set this option to a true value.
peek(...)
This function has exactly the same syntax as sysread(), and
performs nearly the same task (reading data from the socket) but
will not advance the read position so that successive calls to
peek() with the same arguments will return the same results. This
function requires OpenSSL 0.9.6a or later to work.
pending()
This function will let you know how many bytes of data are
immediately ready for reading from the socket. This is especially
handy if you are doing reads on a blocking socket or just want to
know if new data has been sent over the socket.
get_cipher()
Returns the string form of the cipher that the IO::Socket::SSL
object is using.
dump_peer_certificate()
Returns a parsable string with select fields from the peer SSL
certificate. This method directly returns the result of the
dump_peer_certificate() method of Net::SSLeay.
peer_certificate($field)
If a peer certificate exists, this function can retrieve values
from it. If no field is given the internal representation of
certificate from Net::SSLeay is returned. The following fields can
be queried:
authority (alias issuer)
The certificate authority which signed the certificate.
owner (alias subject)
The owner of the certificate.
commonName (alias cn) - only for Net::SSLeay version >=1.30
The common name, usually the server name for SSL
certificates.
subjectAltNames - only for Net::SSLeay version >=1.33
Alternative names for the subject, usually different names
for the same server, like example.org, example.com,
*.example.com.
It returns a list of (typ,value) with typ GEN_DNS,
GEN_IPADD etc (these constants are exported from
IO::Socket::SSL). See
Net::SSLeay::X509_get_subjectAltNames.
get_servername
This gives the name requested by the client if Server Name
Indication (SNI) was used.
verify_hostname($hostname,$scheme)
This verifies the given hostname against the peer certificate using
the given scheme. Hostname is usually what you specify within the
PeerAddr.
Verification of hostname against a certificate is different between
various applications and RFCs. Some scheme allow wildcards for
hostnames, some only in subjectAltNames, and even their different
wildcard schemes are possible.
To ease the verification the following schemes are predefined:
ldap (rfc4513), pop3,imap,acap (rfc2995), nntp (rfc4642)
Simple wildcards in subjectAltNames are possible, e.g.
*.example.org matches www.example.org but not
lala.www.example.org. If nothing from subjectAltNames match
it checks against the common name, but there are no
wildcards allowed.
http (rfc2818), alias is www
Extended wildcards in subjectAltNames and common name are
possible, e.g. *.example.org or even www*.example.org. The
common name will be only checked if no names are given in
subjectAltNames.
smtp (rfc3207)
This RFC doesn't say much useful about the verification so
it just assumes that subjectAltNames are possible, but no
wildcards are possible anywhere.
none No verification will be done. Actually is does not make
any sense to call verify_hostname in this case.
The scheme can be given either by specifying the name for one of
the above predefined schemes, or by using a hash which can have the
following keys and values:
check_cn: 0|'always'|'when_only'
Determines if the common name gets checked. If 'always' it
will always be checked (like in ldap), if 'when_only' it
will only be checked if no names are given in
subjectAltNames (like in http), for any other values the
common name will not be checked.
wildcards_in_alt: 0|'leftmost'|'anywhere'
Determines if and where wildcards in subjectAltNames are
possible. If 'leftmost' only cases like *.example.org will
be possible (like in ldap), for 'anywhere' www*.example.org
is possible too (like http), dangerous things like but
www.*.org or even '*' will not be allowed.
wildcards_in_cn: 0|'leftmost'|'anywhere'
Similar to wildcards_in_alt, but checks the common name.
There is no predefined scheme which allows wildcards in
common names.
callback: \&coderef
If you give a subroutine for verification it will be called
with the arguments
($hostname,$commonName,@subjectAltNames), where hostname is
the name given for verification, commonName is the result
from peer_certificate('cn') and subjectAltNames is the
result from peer_certificate('subjectAltNames').
All other arguments for the verification scheme will be
ignored in this case.
next_proto_negotiated()
This method returns the name of negotiated protocol - e.g.
'http/1.1'. It works for both client and server side of SSL
connection.
NPN support is available with Net::SSLeay 1.46+ and openssl-1.0.1+.
To check support you might call "IO::Socket::SSL-"can_npn()>.
errstr()
Returns the last error (in string form) that occurred. If you do
not have a real object to perform this method on, call
IO::Socket::SSL::errstr() instead.
For read and write errors on non-blocking sockets, this method may
include the string "SSL wants a read first!" or "SSL wants a write
first!" meaning that the other side is expecting to read from or
write to the socket and wants to be satisfied before you get to do
anything. But with version 0.98 you are better comparing the global
exported variable $SSL_ERROR against the exported symbols
SSL_WANT_READ and SSL_WANT_WRITE.
opened()
This returns false if the socket could not be opened, 1 if the
socket could be opened and the SSL handshake was successful done
and -1 if the underlying IO::Handle is open, but the SSL handshake
failed.
IO::Socket::SSL->start_SSL($socket, ... )
This will convert a glob reference or a socket that you provide to
an IO::Socket::SSL object. You may also pass parameters to
specify context or connection options as with a call to new(). If
you are using this function on an accept()ed socket, you must set
the parameter "SSL_server" to 1, i.e.
IO::Socket::SSL->start_SSL($socket, SSL_server => 1). If you have
a class that inherits from IO::Socket::SSL and you want the $socket
to be blessed into your own class instead, use
MyClass->start_SSL($socket) to achieve the desired effect.
Note that if start_SSL() fails in SSL negotiation, $socket will
remain blessed in its original class. For non-blocking sockets
you better just upgrade the socket to IO::Socket::SSL and call
accept_SSL or connect_SSL and the upgraded object. To just upgrade
the socket set SSL_startHandshake explicitly to 0. If you call
start_SSL w/o this parameter it will revert to blocking behavior
for accept_SSL and connect_SSL.
If given the parameter "Timeout" it will stop if after the timeout
no SSL connection was established. This parameter is only used for
blocking sockets, if it is not given the default Timeout from the
underlying IO::Socket will be used.
stop_SSL(...)
This is the opposite of start_SSL(), e.g. it will shutdown the SSL
connection and return to the class before start_SSL(). It gets the
same arguments as close(), in fact close() calls stop_SSL() (but
without downgrading the class).
Will return true if it succeeded and undef if failed. This might be
the case for non-blocking sockets. In this case $! is set to EAGAIN
and the ssl error to SSL_WANT_READ or SSL_WANT_WRITE. In this case
the call should be retried again with the same arguments once the
socket is ready is until it succeeds.
IO::Socket::SSL->new_from_fd($fd, ...)
This will convert a socket identified via a file descriptor into an
SSL socket. Note that the argument list does not include a "MODE"
argument; if you supply one, it will be thoughtfully ignored (for
compatibility with IO::Socket::INET). Instead, a mode of '+<' is
assumed, and the file descriptor passed must be able to handle such
I/O because the initial SSL handshake requires bidirectional
communication.
IO::Socket::SSL::set_default_context(...)
You may use this to make IO::Socket::SSL automatically re-use a
given context (unless specifically overridden in a call to new()).
It accepts one argument, which should be either an IO::Socket::SSL
object or an IO::Socket::SSL::SSL_Context object. See the
SSL_reuse_ctx option of new() for more details. Note that this
sets the default context globally, so use with caution (esp. in
mod_perl scripts).
IO::Socket::SSL::set_default_session_cache(...)
You may use this to make IO::Socket::SSL automatically re-use a
given session cache (unless specifically overridden in a call to
new()). It accepts one argument, which should be an
IO::Socket::SSL::Session_Cache object or similar (e.g something
which implements get_session and add_session like
IO::Socket::SSL::Session_Cache does). See the SSL_session_cache
option of new() for more details. Note that this sets the default
cache globally, so use with caution.
IO::Socket::SSL::set_defaults(%args)
With this function one can set defaults for all SSL_* parameter
used for creation of the context, like the SSL_verify* parameter.
mode - set default SSL_verify_mode
callback - set default SSL_verify_callback
scheme - set default SSL_verifycn_scheme
name - set default SSL_verifycn_name
If not given and scheme is hash reference with key callback
it will be set to 'unknown'
The following methods are unsupported (not to mention futile!) and
IO::Socket::SSL will emit a large CROAK() if you are silly enough to
use them:
truncate
stat
ungetc
setbuf
setvbuf
fdopen
send/recv
Note that send() and recv() cannot be reliably trapped by a tied
filehandle (such as that used by IO::Socket::SSL) and so may send
unencrypted data over the socket. Object-oriented calls to these
functions will fail, telling you to use the print/printf/syswrite
and read/sysread families instead.
ERROR HANDLING
If an SSL specific error occurs the global variable $SSL_ERROR will be
set. If the error occurred on an existing SSL socket the method
"errstr" will give access to the latest socket specific error. Both
$SSL_ERROR and "errstr" method give a dualvar similar to $!, e.g.
providing an error number in numeric context or an error description in
string context.
NON-BLOCKING I/O
If you have a non-blocking socket, the expected behavior on read,
write, accept or connect is to set $! to EAGAIN if the operation can
not be completed immediately.
With SSL there are cases, like with SSL handshakes, where the write
operation can not be completed until it can read from the socket or
vice versa. In these cases $! is set to EGAIN like expected, and
additionally $SSL_ERROR is set to either SSL_WANT_READ or
SSL_WANT_WRITE. Thus if you get EAGAIN on a SSL socket you must check
$SSL_ERROR for SSL_WANT_* and adapt your event mask accordingly.
Using readline on non-blocking sockets does not make much sense and I
would advise against using it. And, while the behavior is not
documented for other IO::Socket classes, it will try to emulate the
behavior seen there, e.g. to return the received data instead of
blocking, even if the line is not complete. If an unrecoverable error
occurs it will return nothing, even if it already received some data.
SNI Support
Newer extensions to SSL can distinguish between multiple hostnames on
the same IP address using Server Name Indication (SNI).
Support for SNI on the client side was added somewhere in the OpenSSL
0.9.8 series, but only with 1.0 a bug was fixed when the server could
not decide about its hostname. Therefore client side SNI is only
supported with OpenSSL 1.0 or higher in IO::Socket::SSL. With a
supported version, SNI is used automatically on the client side, if it
can determine the hostname from "PeerAddr" or "PeerHost". On
unsupported OpenSSL versions it will silently not use SNI. The
hostname can also be given explicitly given with "SSL_hostname", but in
this case it will throw in error, if SNI is not supported. To check
for support you might call "IO::Socket::SSL-"can_client_sni()>.
On the server side earlier versions of OpenSSL are supported, but only
together with Net::SSLeay version >= 1.50. To check for support you
might call "IO::Socket::SSL-"can_server_sni()>. If server side SNI is
supported, you might specify different certificates per host with
"SSL_cert*" and "SSL_key*", and check the requested name using
"get_servername".
RETURN VALUES
A few changes have gone into IO::Socket::SSL v0.93 and later with
respect to return values. The behavior on success remains unchanged,
but for all functions, the return value on error is now an empty
list. Therefore, the return value will be false in all contexts, but
those who have been using the return values as arguments to subroutines
(like "mysub(IO::Socket::SSL(...)-"new, ...)>) may run into problems.
The moral of the story: always check the return values of these
functions before using them in any way that you consider meaningful.
DEBUGGING
If you are having problems using IO::Socket::SSL despite the fact that
can recite backwards the section of this documentation labelled 'Using
SSL', you should try enabling debugging. To specify the debug level,
pass 'debug#' (where # is a number from 0 to 3) to IO::Socket::SSL when
calling it. The debug level will also be propagated to
Net::SSLeay::trace, see also Net::SSLeay:
use IO::Socket::SSL qw(debug0);
No debugging (default).
use IO::Socket::SSL qw(debug1);
Print out errors from IO::Socket::SSL and ciphers from Net::SSLeay.
use IO::Socket::SSL qw(debug2);
Print also information about call flow from IO::Socket::SSL and
progress information from Net::SSLeay.
use IO::Socket::SSL qw(debug3);
Print also some data dumps from IO::Socket::SSL and from
Net::SSLeay.
EXAMPLES
See the 'example' directory.
BUGS
IO::Socket::SSL depends on Net::SSLeay. Up to version 1.43 of
Net::SSLeay it was not thread safe, although it did probably work if
you did not use SSL_verify_callback and SSL_password_cb.
If you use IO::Socket::SSL together with threads you should load it
(e.g. use or require) inside the main thread before creating any other
threads which use it. This way it is much faster because it will be
initialized only once. Also there are reports that it might crash the
other way.
Creating an IO::Socket::SSL object in one thread and closing it in
another thread will not work.
IO::Socket::SSL does not work together with
Storable::fd_retrieve/fd_store. See BUGS file for more information and
how to work around the problem.
Non-blocking and timeouts (which are based on non-blocking) are not
supported on Win32, because the underlying IO::Socket::INET does not
support non-blocking on this platform.
If you have a server and it looks like you have a memory leak you might
check the size of your session cache. Default for Net::SSLeay seems to
be 20480, see the example for SSL_create_ctx_callback for how to limit
it.
The default for SSL_verify_mode on the client is currently
SSL_VERIFY_NONE, which is a very bad idea, thus the default will change
in the near future. See documentation for SSL_verify_mode for more
information.
LIMITATIONS
IO::Socket::SSL uses Net::SSLeay as the shiny interface to OpenSSL,
which is the shiny interface to the ugliness of SSL. As a result, you
will need both Net::SSLeay and OpenSSL on your computer before using
this module.
If you have Scalar::Util (standard with Perl 5.8.0 and above) or
WeakRef, IO::Socket::SSL sockets will auto-close when they go out of
scope, just like IO::Socket::INET sockets. If you do not have one
of these modules, then IO::Socket::SSL sockets will stay open until the
program ends or you explicitly close them. This is due to the fact
that a circular reference is required to make IO::Socket::SSL sockets
act simultaneously like objects and glob references.
DEPRECATIONS
The following functions are deprecated and are only retained for
compatibility:
context_init()
use the SSL_reuse_ctx option if you want to re-use a context
socketToSSL() and socket_to_SSL()
use IO::Socket::SSL->start_SSL() instead
kill_socket()
use close() instead
get_peer_certificate()
use the peer_certificate() function instead. Used to return
X509_Certificate with methods subject_name and issuer_name. Now
simply returns $self which has these methods (although deprecated).
issuer_name()
use peer_certificate( 'issuer' ) instead
subject_name()
use peer_certificate( 'subject' ) instead
SEE ALSO
IO::Socket::INET, IO::Socket::INET6, IO::Socket::IP, Net::SSLeay.
AUTHORS
Steffen Ullrich, <steffen at genua.de> is the current maintainer.
Peter Behroozi, <behrooz at fas.harvard.edu> (Note the lack of an "i"
at the end of "behrooz")
Marko Asplund, <marko.asplund at kronodoc.fi>, was the original author
of IO::Socket::SSL.
Patches incorporated from various people, see file Changes.
COPYRIGHT
The original versions of this module are Copyright (C) 1999-2002 Marko
Asplund.
The rewrite of this module is Copyright (C) 2002-2005 Peter Behroozi.
Versions 0.98 and newer are Copyright (C) 2006-2013 Steffen Ullrich.
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
Appendix: Using SSL
If you are unfamiliar with the way OpenSSL works, good references may
be found in both the book "Network Security with OpenSSL" (Oreilly &
Assoc.) and the web site
<http://www.tldp.org/HOWTO/SSL-Certificates-HOWTO/>;. Read on for a
quick overview.
The Long of It (Detail)
The usual reason for using SSL is to keep your data safe. This means
that not only do you have to encrypt the data while it is being
transported over a network, but you also have to make sure that the
right person gets the data. To accomplish this with SSL, you have to
use certificates. A certificate closely resembles a Government-issued
ID (at least in places where you can trust them). The ID contains
some sort of identifying information such as a name and address, and is
usually stamped with a seal of Government Approval. Theoretically,
this means that you may trust the information on the card and do
business with the owner of the card. The same ideas apply to SSL
certificates, which have some identifying information and are "stamped"
[most people refer to this as signing instead] by someone (a
Certificate Authority) who you trust will adequately verify the
identifying information. In this case, because of some clever number
theory, it is extremely difficult to falsify the stamping
process. Another useful consequence of number theory is that the
certificate is linked to the encryption process, so you may encrypt
data (using information on the certificate) that only the certificate
owner can decrypt.
What does this mean for you? It means that at least one person in the
party has to have an ID to get drinks :-). Seriously, it means that
one of the people communicating has to have a certificate to ensure
that your data is safe. For client/server interactions, the server
must always have a certificate. If the server wants to verify that
the client is safe, then the client must also have a personal
certificate. To verify that a certificate is safe, one compares the
stamped "seal" [commonly called an encrypted digest/hash/signature] on
the certificate with the official "seal" of the Certificate Authority
to make sure that they are the same. To do this, you will need the
[unfortunately named] certificate of the Certificate Authority. With
all these in hand, you can set up a SSL connection and be reasonably
confident that no-one is reading your data.
The Short of It (Summary)
For servers, you will need to generate a cryptographic private key and
a certificate request. You will need to send the certificate request
to a Certificate Authority to get a real certificate back, after which
you can start serving people. For clients, you will not need anything
unless the server wants validation, in which case you will also need a
private key and a real certificate. For more information about how
to get these, see <http://www.modssl.org/docs/2.8/ssl_faq.html#ToC24>;.
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